The height of an electronic component to be mounted is one of the important parameters for a mounter. To be more specific, if the actual height of an electronic component held by a transfer head for mounting it is different from a value assigned to the electronic component and stored for controlling the mounter, various types of problems occur when mounting the electronic component onto a board. For example, in the case where the actual height of an electronic component is less than the stored data, the electronic component is released before it reaches the board, and thus it may not be mounted in the right position on the board. Conversely, if the actual height of an electronic component is greater than the stored data, the electronic component is pressed against the board too strongly that the board, the electronic component or the nozzle may be damaged.
Conventionally, in order to enter height data of an electronic component into a mounter, the height data of the electronic component is obtained from the electronic component manufacturer and entered manually, or the electronic component is taken from a tape or the like for holding electronic components and measured using a slide caliper and the like, and the measured value is entered manually.
However, an electronic component may vary in its height depending on manufacturers or manufacturing lots even if its performance is unchanged. For example, when currently used components run out of stock under a situation where the lead time, from receipt of order of board production until shipping of the boards, is reduced, there is no choice but to use substitute components from another manufacturer. In such a case, the data of the substitute components has to be entered manually even if the performance of the components is unchanged. Such data entry is not only very troublesome but also causes measurement error or human error in the case where the height of a substitute component is measured and the data of the component is entered manually, and thus causes a discrepancy between the actual height of the component and the entered data.
So, in order to avoid measurement error and human error and ensure a precise match between the actual height of an electronic component and the data stored in a mounter, a patent application for a mounter as shown in FIG. 1 including a detector for detecting the size of a component so as to obtain and store the size of the component automatically has been filed (see, for example, Japanese Laid-Open Patent Application No. 07-38294).
In recent years, a so-called multifunction mounter which mounts a variety of electronic components ranging from tiny components to larger ones on its own has been widely used.
If a detector for detecting the size, in particular, the height of a component, is applied to such a multifunction mounter, the following problems occur. If a detector is attached to a transfer head of a mounter, it becomes possible to measure the height of a component during a period from when the transfer head picks up the component by suction until it moves above the board, and therefore the measurement of the height gives rise to no loss in takt time. On the other hand, a large-sized detector is needed to detect the height of a larger component. If such a detector is attached to the transfer head of the mounter, the size and weight of the detector burden the transfer head which moves at a high speed to mount components, and thus the positioning accuracy of the transfer head cannot be maintained.
Furthermore, since a large-sized detector has generally a low resolution, if this detector measures the height of a tiny component, the measurement error for the height is too large to mount the component without any problem. A large-sized detector with a high resolution unnecessarily leads to rise in cost.